Learn Hardcore Korean: gakkeum gichayeogeseo chingureul mannayo. - I sometimes meet a friend at the train station.

가끔 is an adverb meaning “sometimes” or “occasionally.” It’s used to describe actions that don’t happen all the time but occur from time to time.

What is 기차역?

기차역 is a compound noun made of 기차 (train) + 역 (station). Together, 기차역 means “train station.”

Why is 에서 used with 기차역 instead of 에?

The particle -에서 marks where an action takes place. Since 만나요 (“meet”) is an action, you use 기차역에서 to say “at the train station.”
By contrast, -에 marks a destination or static location and is used with verbs like 있다 (“to be/exist”) or 가다 (“to go”).

Why is 친구 marked with 를 (as 친구를 만나요)?

The particle -를 (or -을 after a consonant) marks the direct object of a verb. Here, 친구 (“friend”) is what you meet, so you attach -를 to show it’s the object of 만나다.

Why is there no subject like 저 or 저는 in this sentence?